This application claims priority based on German Utility Model No. 100 48 911.7, filed Oct. 2, 2000, the entire disclosure of which is incorporated herein by reference.
This invention relates to a process for determining absolute position with steering path and steering angle sensors, as well as a circuit configuration for implementing the process.
Processes and devices of this type are known from DE 32 46 959 C3. The measuring device described therein uses two mechanically coupled individual sensors for determining absolute position, of which the first in the measuring range generates an output signal D1 with a first number n of periods and the second in the same measuring range generates an output signal D2 with a second number n-1 of periods, in which a differential signal is generated for generating a monotone, clear, absolute position signal. In addition, a third sensor with a third number of periods is used, which generates a third number of periods which differs from the first and the second number of periods.
DE 198 49 554 C1 describes two mechanical individual sensors which are coupled with a rotating shaft, of which the first sensor in the measuring range generates an output signal "PHgr"1 with a first number k1 of periods, and the second sensor in the same measuring range generates an output signal "PHgr"2 with a second number k2 of periods, in which the two number of periods differ by one. A differential signal is generated by means of the two signals "PHgr"1 and "PHgr"2, to which applies 0xe2x89xa6"PHgr"1, "PHgr"2xe2x89xa62xcfx80. Then it is tested whether the differential signal is negative, and if this is the case, a constant value (2xcfx80) is added to the differential signal to generate a corrected differential signal. The corrected differential signal, which is multiplied by the number of periods k1 and divided by the measuring range 2xcfx80, is rounded off to the next lower integer, and subsequently this value is multiplied by the measuring range 2xcfx80, to generate a period number signal. The output signal "PHgr"1 of one sensor is added to this period number signal, to generate a very precise, absolute output signal. Furthermore, an auxiliary signal is generated as difference between the very precise, absolute output signal and the corrected differential signal multiplied by the period number k1 of one sensor, and whether this auxiliary signal lies within predetermined limit values (+/xe2x88x92n) is checked. If the auxiliary signal lies outside the limit values, another correction is performed of the corrected, very precise, absolute output signal by adding or subtracting a given value (2xcfx80).
In summary, with this prior art, a period number PNr with the value range 0xe2x89xa6PNrxe2x89xa6k1xe2x88x921 is obtained from the signal difference of the two sensors. By combining the period number PNr with the periodic output signal of a sensor one obtains a monotone, clear and thus absolutely valid measuring result within the measuring range.
If one of the sensor modules fails, the system no longer functions properly, which is problematic with safety-related applications, such as steering angle sensors with motor vehicles.
In view of the foregoing, it is the object of the present invention to provide an improvement of the process and device mentioned hereinabove, in that in the case of failure of a sensor module, said device provides a sufficiently precise function. The foregoing object is achieved in the present invention by means of the features specified herein. Advantageous inventive embodiments and improvements can be concluded from the dependent claims.
A basic principle of the invention is to provide a third sensor which also is mechanically coupled with the two other sensors and in the measuring range is provided with a number k3 of periods, in which k2=k1xe2x88x92xc2xd=k2+xc2xd applies. By selecting the number of periods k3 one achieves that the phase difference to the other two sensors for each position within the measuring range is equal in terms of value. If an error occurs at one of the two first sensors, one can fall back upon the third sensor, in that the relevant period number is determined from the phase difference with the remaining functional sensor analogous to the process described in DE 198 49 554 C1.
With this invention, the system remains functional, even if one of the two other main sensor modules fails and, at least, it allows an emergency operation. As far as the system response is concerned, there is no difference whether the first or second sensor fails. During emergency operation a reduced measuring precision is not permissible. The emergency operation can be detected, so that the sensor system can conveniently be maintained and replaced.
Alternatively, the invention may comprise various other methods and apparatuses.
Other features will be in part apparent and in part pointed out hereinafter.